Since PCOS is related to an insulin resistance, if you are overweight, a moderate amount of weight loss can help improve your condition. Adding 15-30 minutes of exercise, even if its just walking, can help improve your bodies hormone sensitivity.
Including foods that will help keep your blood sugar stable, will help decrease symptoms. Use foods like sweet potatoes, legumes, dark leafy greens, raw oats, almond butter, edamame beans (in moderation), hemp seeds, chia seeds, spirulina, watercress and flax seeds to keep blood sugar stable. These are all safe to eat when breastfeeding.
Looking at your current diet and eliminating refined carbohydrates like white breads, white rice, pastas and sodas, processed foods and sweets can also help improve insulin resistance. It is beneficial to not consume things like contaminated fish, non organic dairy (may be best to avoid dairy completely as to not introduce added hormones), drinking from BPA free bottles and not using BPA plastics and canned foods.
If you are into alternative medicine, here is a Traditional Chinese Medicine approach:
(there are some great dietary suggestions at the end of this page)
I also wanted to recommend this site for more information!